V899 Mon: A Peculiar Eruptive Young Star Close to the End of Its Outburst

Abstract

The eruptive young star V899 Mon shows characteristics of both FUors and EXors. It reached a peak brightness in 2010, then briefly faded in 2011, followed by a second outburst. We conducted multifilter optical photometric monitoring, as well as optical and near-infrared spectroscopic observations, of V899 Mon. The light curves and color–magnitude diagrams show that V899 Mon has been gradually fading after its second outburst peak in 2018, but smaller accretion bursts are still happening. Our spectroscopic observations taken with Gemini/IGRINS and VLT/MUSE show a number of emission lines, unlike during the outbursting stage. We used the emission line fluxes to estimate the accretion rate and found that it has significantly decreased compared to the outbursting stage. The mass-loss rate is also weakening. Our 2D spectroastrometric analysis of emission lines recovered jet and disk emission of V899 Mon. We found that the emission from permitted metallic lines and the CO bandheads can be modeled well with a disk in Keplerian rotation, which also gives a tight constraint for the dynamical stellar mass of 2 M ⊙. After a discussion of the physical changes that led to the changes in the observed properties of V899 Mon, we suggest that this object is finishing its second outburst.

Photometric and Spectroscopic Study of the EXor-like Eruptive Young Star Gaia19fct

“…The obtained T ex and N H2 are 1640 ± 236 K and (7.6 ± 4.5) × 10 6 cm −2 , respectively. The obtained T ex is lower than found for other eruptive young stars (V346 Nor and V899 Mon; Kóspál et al 2020;Park et al 2021a), suggesting that the T ex of the shock-heated region in Gaia19fct is lower than in these two targets. The electron density (n e ) and electron temperature (T e ) of the jet/outflow region can be estimated using the [Fe II] line ratios.…”

“…Weak CO overtone band head features superimposed with absorption profiles were observed in 2020 November. The CO overtone emission features are typically found in EXors and EXor-like objects (Kóspál et al 2011;Hodapp et al 2019Hodapp et al , 2020Park et al 2021a;Cruz-Sáenz de Miera et al 2022a). To study the physical properties (T ex and N CO ) where these CO features are formed, we fitted a simple slab model for the emission and absorption components separately and found the best-fit results (Section 4.4.7).…”

“…Several H 2 emission lines were observed in 2020 November (Figure 7), which are rarely detected in FUors or EXors. Only about 10% of eruptive stars showed H 2 rovibrational transitions: V1647 Ori (Aspin 2011), PTF 10nvg (Hillenbrand et al 2013), Gaia19ajj (Hillenbrand et al 2019), V960 Mon (Park et al 2020), Gaia19bey (Hodapp et al 2020), V346 Nor (Kóspál et al 2020), and V899 Mon (Park et al 2021a). The mean and standard deviation of the peak velocity is −5 ± 1 km s −1 , slightly blueshifted with respect to the systemic velocity.…”

“…We constructed an excitation diagram (Figure 8) to estimate the gas excitation temperature (T ex ) and the column density (N H2 ) of H 2 lines (van den Ancker et al 1999;Fernandes 2000;Nisini et al 2002;Davis et al 2011;Oh et al 2018;Park et al 2021a). The excitation diagram can be fitted by a single straight line if the gas is thermalized with a single temperature.…”

“…The varying ratio of the emission and absorption components suggested that the temperature and column density of the emitting and absorbing material are different. To quantify this, we used a simple isothermal slab model to calculate the expected CO overtone feature spectrum for a grid of different excitation temperatures (T) and CO column densities (N CO ), following the approach described in Kóspál et al (2011) andPark et al (2021a). For this analysis, we fitted both IGRINS spectra separately to provide ranges of the obtained physical parameters.…”